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My understanding is this type of system is illegal in Canada.

Is it because of this rule only, or are there others?

10-106 Alternating-current systems (see Appendix B)
(1) Except as otherwise provided for in this Code, alternating-current systems shall be grounded if
(a) by so doing, their maximum voltage-to-ground does not exceed 150 V; or
(b) the system incorporates a neutral conductor.
(2) Wiring systems supplied by an ungrounded supply shall be equipped with a suitable ground fault detection
device to indicate the presence of a ground fault.
That basically seems to suggest that you could have one if it was less than 150v to ground, but nobody would find that useful so it doesn't get used. On the other hand, 10-210 does make reference to such a system, so it must exist somewhere.

10-210 Conductor to be grounded
(1) For alternating-current wiring systems, the conductor to be grounded shall be as follows:
(a) single-phase, 2-wire — the identified conductor;
(b) single-phase, 3-wire — the identified neutral conductor;
(c) multi-phase systems having one wire common to all phases — the identified neutral conductor;
(d) multi-phase systems having one phase grounded — the identified conductor; and
(e) multi-phase systems in which one phase is used as in Item (b) — the identified conductor.
(2) In multi-phase systems in which one phase is used as a single-phase 3-wire system, only one phase shall be
grounded.
I realise there are drawbacks to the corner grounded delta, but I was just wondering out of curiosity because sometimes people from the states post about them here. The only deltas I've ever seen have been ungrounded and only in "serious" industrial locations.
 

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Regarding 10-106, we've got a similar rule in the states. Grounding stabilizes system voltage, so if by grounding it you can keep the L-G voltage at 150V or less, then you must ground it.

If grounding it would not give you less than 150V to ground (e.g., on a 240VΔ or 480VΔ) then it is not required to be grounded.

Regarding 10-210, the idea is that if you have a system like that 240VΔ it's often better if grounded. The easiest way to accomplish that is to just corner ground a phase conductor.
 
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